Gears, belt chains, plane and roller bearings, linear bearings, sleeve bearings, pulleys, sliding plates and other similar devices have long been used to transmit, communicate, or facilitate motion and power in mechanical devices. Materials that are useful in such applications must be resilient and tough to withstand the dynamic application of force and repetitive strain. It is also desirable that such materials be amenable to machining or processing. This is particularly true in the case of precision applications such as the manufacture of gears for instrumentation. The tribological properties of the material are of further and perhaps more important consideration.
Using the gear as an example of such devices, failure can result when the material cannot properly hold a tolerance, from the inability to withstand the torsional stresses of start-up and shut-down, and from cyclical fatigue. These problems result in a failure of the tooth from excessive wear which can be compounded by plastic flow or creep due to thermal softening. Additionally, tooth bending fatigue, contact fatigue (pitting and spalling), thermal fatigue, tooth bending impact, tooth shear, tooth clipping, case crushing, torsional shear, and stress ruptures have similar impact. The role of material selection and preparation thus clearly have much to do with the successful design of a motion and power transmission strategy.
Metals such as steel, bronze, and aluminum alloys have been successfully used in a wide variety of such applications. However, the use of nonmetal engineering materials such as polymers has greatly improved noise reduction, vibration damping, and economics in many cases. Unfortunately, using a polymeric power or motion transmitting means such as a gear is not without its drawbacks. Low heat resistance, large thermal deformation, large shrinkage upon processing, and mediocre mechanical strength have precluded the use of numerous thermoplastics, thermosets, and resins from serious consideration in demanding applications.
It is a general practice in the art not to communicate power and motion from one such polymeric article to another of similar composition. This is particularly true where the stress on the article is significant. Polyacetal and Nylon 66 are typical materials used in gearing arrangements and other similar applications where nonmetals are used. One will often find, for example, a polyacetal pinion and a nylon spur gear in communication with one another. However, in most nontrivial translations of power and motion, one will rarely find combinations involving similar materials as such combinations generally result in disappointing wear factors. Of course, finding the right combination of materials to use together and sourcing such dissimilar materials creates economic inefficiencies and other problems.
While these considerations clearly apply to the structure and manufacture of gears, it should also be borne in mind that almost any device used to transmit, communicate, or facilitate power and motion necessarily involves similar concerns. For example, cams are generally used to communicate motion and power by means of a connection between an edge (or a groove therein) or surface and a follower. In addition to repetitive/cyclic movement and imposition of force acting on both cam and follower, these mechanisms are often designed to incorporate large accelerations. Thus, the use of materials which cannot hold a tolerance (e.g., through loss of material) or which are not amenable to precision processing or manufacture can easily result in wildly eccentric motion and, ultimately, failure. It is therefore important to employ materials which can be worked to precision, which function well when placed in communication with each other, and which can withstand repetitive/cyclic movement and impact.
The same can be said of bearings with rolling or sliding contact. The repetitive and cyclic facilitation of motion inevitably raises concerns analogous to those of gears and cams. Indeed, one skilled in the art will readily appreciate that from a materials perspective, an improvement in a means for transmitting power and motion is generally applicable to all means of power and motion transmission.
Rolling contact and sliding contact are manifested in most power and motion gear applications. Rolling contact predominates in motion and power transmission when such applications are between parallel shafts or between intersecting shafts. When non-parallel and non-intersecting shafts are employed, sliding contact predominates. Thus, materials useful in power and motion transmission between all shaft setups exhibit both good wear and good strength.
Polyketones have heretofore not been used commercially in such applications. These polymers of carbon monoxide and olefins are now well known in the art. They are disclosed in numerous patents assigned to Shell Oil Company which are exemplified by U.S. Pat. No. 4,880,865 and U.S. Pat. No. 4,818,811 which are herein incorporated by reference. The introduction of power and motion translating means which could further improve the utility and economics of machine design and manufacture as well as the performance of existing designs would be welcome. Accordingly, this is an object of the invention.